Tire sealant compounds have long been used in pneumatic tires. One type of tire sealant is injected into a flat tire and inflates/seals the tire. These short-term types tire sealants are intended as an emergency measure, to be injected into the tire through the valve stem after a puncture occurs, and do not remain active for extended periods of time after placement in the tire. Known sealant compositions of this type include water-based latexes, which are effective for only a short time, because they dry by evaporation and coagulation, leaving a rubbery mass. Another type of short-term tire sealant employs a solution of sodium silicate or cellulosic material which dry to form a sealing plug. Solutions of dextrin and similar organic gums have also been used. All of these compositions have the shortcoming that they dry after a relatively short period of time, and therefore cannot be used for permanent or long-term protection from punctures, but rather are normally applied after a puncture occurs.
Another type of tire sealant is a preventative sealant that is used on the innerliner of the tire and reacts to punctures by sealing them on an as-needed basis. One of the most common long-term tire sealants includes a glycol ether carrier liquid (typically ethylene glycol or polypropylene glycol) with suspended fibers of glass and/or cellulose. An example of this type of sealant is disclosed in U.S. Pat. No. 4,337,322. This patent teaches the making of a sealant composition using the following ingredients: asbestos fibers, ethylene glycol monomer, polyethylene glycol, polyisoprene, process oil, detergent, sodium bicarbonate and water. This type of sealant has several drawbacks. First, ethylene glycol ethers are potentially poisonous and toxic, the combination of which makes the material very dangerous for consumer applications. A second disadvantage is that the freezing points of glycol ethers have a wide range from −13° C. to −97° C. and the viscosity of glycol ethers varies greatly between −5° C. and 25° C. Because the temperature of a vehicle tire in use may vary from below −29° C. to above 50° C., the practical effective temperature range of sealant mixtures based on glycol ethers is limited.
At least one tire sealant claims an environmentally safe product. This tire sealant is disclosed in U.S. Pat. No. 5,059,636, which teaches the making of a sealant composition including: finely ground rubber, calcium chloride, wheat flour, water, sodium nitrite, vegetable oil and a defoaming agent. The use of vegetable oil in this composition is to emulsify the mixture so that the ingredients of the product do not separate upon mixing. The calcium chloride serves to lower the freezing point of the sealant so that it remains operative at temperatures as low as −30° F. However, a problem with this sealant is that the calcium chloride reacts with the metal wheel resulting in corrosion.
Another problem with tire sealants is that many contain materials that may become combustible during a tire retreading process. Prior to retreading a tire, any tire sealant on the innerliner must be removed and is typically washed out with water. Some of the sealant materials often remain on the innerliner and dry. During the retreading process, a tire tread is cured to the tire in an autoclave chamber under elevated pressure and temperature conditions. The temperatures typically range from 212–260 degrees Fahrenheit depending on whether the tread has been pre-cured. Any remaining sealant materials dried on the tire innerliner are subjected to the elevated temperature and pressure. If these sealant materials are combustible, such as cellulose fibers, it is possible for a chamber fire to occur.
Accordingly, there is a need for an effective tire sealant composition comprising an environmentally safe carrier fluid material where the material will flow at very low temperatures (−30° F., −34.4° C.) without freezing, and wherein the material will not react with a wheel and cause corrosion and will not support combustion in the tire retreading process after it is dry inside the tire.